Hybodus enters the LRT as one of our direct ancestors

It should come as no surprise
that Hybodus was basal to the spiny sharks (Acanthodii, Fig. 2). Just look at those homologous dorsal spines (Fig. 1). These taxa are also transitional from chimaeras to lobefins + humans in the LRT. So they are ‘key players’.

Traditionally considered an odd sort of shark with dorsal spines,
Hybodus (Fig. 1) nests in the large reptile tree (LRT, 1583 taxa; Fig. 2) between sharks + chimaeroids and placoderms leading + two large clades of bony fish. Apparently this hypothesis of interrelationships has been overlooked until now, but it answers so many long-standing questions. Hybodus also greatly resembled the basal placoderm, Coccosteus (Fig. 1) another overlooked hypothesis of interrelationships. And catfish, too.

Hybodus basanus (Agassiz 1837; H. reticulatus (Early Jurassic skull); 2m in length, Permian –Late Cretaceous) nests between sharks + chimaeroids and spiny sharks + bony fish. This relationship was overlooked until now. Note the spines on the dorsal fins. These are homologous with spines on spiny sharks like Diplacanthus (below). Spines are transitional betwen fleshy shark fins and transparent ray fins. The skull is also transitional between sharks and bony fish, despite the presence of large gill bars (yellow) lateral to the jaws.

The LRT nests two acanthodians in the stem lobefin clade (Fig. 2).
Earlier we looked at the central nesting of acanthodians between basal taxa and bony fish. Hybodus further confirms this hypothesis of interrelationships now seeking confirmation or refutation from an independent study using a similar taxon list and a new character list.

With more taxa,
and more knowledge of the 137 taxa at hand, note that catfish no longer nest with placoderms, but transitional between placoderms and ray fin fish (Fig. 2).

References
Agassiz L 1837 in Agassiz L. 1833-1843. Recherches sur les Poissons fossiles-I, I, III, Neuchatel, pp 1420.
Burrow C, Blaauwen J, Newman M and Davidson R 2016. The diplacanthid fishes (Acanthodii, Diplacanthiformes, Diplacanthidae) from the Middle Devonian of Scotland. Palaeontologia Electronica 19.1.10A: 1-83.
Davis SP, Finarelli JA and Coates MI 2012. Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes. Nature 486:247–250.
Duff P 1842. Sketch of the Geology of Moray. Forsyth and Young, Elgin
Maisey JG 1983. Cranial anatomy of Hybodus basanus Egerton from the Lower Cretaceous of England. American Museum Novitates 2758:1–64.
Miller H 1841. The Old Red Sandstone. (first edition). Thomas Constable and Sons, Edinburgh.

wiki/Hybodus
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